1. Field of the Invention
The present invention relates to a method for the direct epoxidation of olefins in the liquid phase by reacting the olefin with hydrogen peroxide at a temperature between 0.degree. C. and 120.degree. C. in the presence of a boron containing catalyst while continuously eliminating the water introduced with the hydrogen peroxide as well as the water formed in the course of the reaction by distillation, or azeotropic distillation, or entrainment or by combination with a reagent susceptible to react with water in the reaction conditions.
2. Description of the Prior Art
Epoxidated olefins are important commercially and are used in great quantities as intermediates in the manufacture of urethanes, glycols, surfactants, plasticizers, and the like. However, processes available to the art for the epoxidation of olefins are becoming less and less suitable because they are subject to ecology restrictions while also being uneconomical.
It is well known that the chlorohydrin process, for example, wherein an olefin is reacted with chlorine in an alkaline medium, is unsatisfactory because producing considerable amounts of inorganic and organic chlorinated by-products which are difficult to dispose of and which have limited practical usage.
Another process known to the art which involves lesser pollutants is based on the catalytic epoxidation of an olefin in an anhydrous medium by means of an organic hydroperoxide resulting from the oxidation of a saturated hydrocarbon with molecular oxygen. Production of the epoxide is accompanied, however, by production of at least an equivalent quantity of the alcohol corresponding to the starting hydroperoxide. Production of the latter product presents a problem since it considerably influences the economy of the process.
Because of the inherent disadvantages in prior art processes for catalytic epoxidation of olefins, the industry continues to seek more direct methods for epoxidation of olefins, as well as methods which have a higher yield to avoid the problem of by-products.
Direct epoxidation of olefins by molecular oxygen has been the subject of numerous investigations. Thus far, however, this process has been limitedly used in epoxidation of ethylene with good yields using a silver base catalyst. When this technique is used on other olefins, there is a total lack of selectivity.
Hydrogen peroxide is a useful reactant because of its nature as a non-polluting oxidizing agent. However, its reactivity as an epoxidizing agent in regard to unactivated olefins is low and requires the presence of an activating agent to produce, in situ, a more active percompound. There have been proposed various epoxidation processes using, for example, peracids such as performic, peracetic or perpropionic acid, such as that disclosed in Belgian Pat. No. 838,068. However, because of the instability of epoxides in an acid medium, such processes are particularly difficult to use.
Various catalytic processes have also been described in the art which have the advantage over the above processes of not using stoichiometric quantities of percompounds whose synthesis complicates the process of obtaining epoxides. For example, there has been proposed the use, in an aqueous or water-alcohol medium, of oxides or oxyacids derived from transition metals such as molybdenum, tungsten, vanadium, titanium, and the like. These processes are not satisfactory because the desired epoxide is not obtained, but instead the corresponding glycol or mixtures of products resulting from the opening of the oxirane cycle.
The use of peroxide complexes of some of these transition metals has also been proposed such as the technique described in French Pat. No. 2,082,811. These complexes are good epoxidazing agents but their in situ regeneration presents such a problem that industrial application of the process is not feasible.
Belgian Pat. No. 747,316 discloses the use of hydrogen peroxide as an epoxidizing agent in the presence of a catalyst on a base of an organic derivative of tin. It is difficult, however, to utilize this process on an industrial scale.
In French Pat. No. 2,245,582 there is described a process for the epoxidation of an olefin by means of hydrogen peroxide in the presence of a catalytic system containing at least one derivative of lead and at least one derivative of the elements of Groups IVA, VA, VIA of the Mendeleev Periodic Table.
In French Pat. No. 2,300,765 applicants have described the use of various organic and mineral derivatives of arsenic in conjunction with a derivative of a transition metal belonging to Groups IVA, VA and VIA of the Periodic Table as catalysts for epoxidation of olefins by hydrogen peroxide in liquid phase. Also, there is a more recent proposal in Belgian Pat. No. 838,953 of a method for making oxides of olefins by action of hydrogen peroxide on olefins in the presence of an organic or mineral derivative of arsenic and in the absence of any trace of transition metal. However, in order to obtain good yields, these methods require the use of highly concentrated aqueous solutions of hydrogen peroxide which are not commercially available at present, and the manufacture and handling of which involves serious problems of safety. These major drawbacks are supplemented by the defect of an epoxidation reaction that is certainly effective but very slow and is difficult to economically scale to an industrial production unit.
It has now been found during continuing study of the epoxidation of olefins, that it is easily possible to overcome numerous prior art drawbacks by operating a method for production of olefins by using a boron containing catalyst and a substantial excess of olefin relative to hydrogen peroxide and by continuously eliminating from the reaction medium the water formed in the course of the reaction as well as any water introduced with the hydrogen peroxide either by direct distillation or by azeotropic distillation or by simple entrainment procedures or by combination with a reagent susceptible to react with water in the reaction conditions. Under these conditions, it is found that rates of conversion of the hydrogen peroxide and epoxide selectivities are very high, simply by using commercial aqueous solutions titrating between 30% and 70% by weight of hydrogen peroxide. Furthermore, the boron catalyst is found to have a long life and thereby avoids frequent replacement.